Projectors that use color wheels are disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2012-3213) and Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2013-225089). In addition, an image display device that uses a phosphor wheel is disclosed in Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2015-195564).
Patent Document 1 and Patent Document 2 disclose technology of adjusting the timing of a modulation operation realized by display elements and the rotation timing of a color wheel, and Patent Document 3 discloses a technology of synchronizing the rotation of a phosphor wheel and the drive of a light valve.
When using a color wheel and a phosphor wheel as described above, because these components rotate, synchronization with the drive of other constituent elements becomes crucial.
FIG. 1 is a block diagram showing the configuration of the control system of a projector that is provided with a color wheel and a phosphor wheel, and FIG. 2 shows the configuration of the optical system.
Control unit 103 shown in FIG. 1 controls the rotation operation of phosphor wheel 101 and color wheel 102, the modulation operation of DMD (Digital Micromirror Device) 104, and the output state of semiconductor laser 106 by way of laser drive circuit 105.
Control unit 103 causes phosphor wheel 101 to rotate by means of drive signal S2 and receives as input from phosphor wheel 101 Index signal S1 that indicates the rotational state of phosphor wheel 101. Control unit 103 further causes color wheel 102 to rotate by means of drive signal S4 and receives as input from color wheel 102 Index signal S3 that indicates the rotational state of color wheel 102.
The optical system shown in FIG. 2 is next described.
Laser light supplied from semiconductor laser arrays 106-1 and 106-2 that accommodate a plurality of semiconductor lasers is synthesized by polarization beam splitter 203. Semiconductor laser array 106-1 supplies blue P-polarized laser light, and semiconductor laser array 106-2 supplies blue S-polarized laser light. Polarization beam splitter 203 transmits P-polarized light and reflects S-polarized light, and as a result, the laser light supplied from each of semiconductor laser arrays 106-1 and 106-2 is synthesized by polarization beam splitter 203 and applied as input in a high-intensity state to polarization beam splitter 205 by way of mirror 204 and polarization conversion device 202.
Polarization conversion device 202 is a component that combines a polarization beam splitter, a mirror, and a half-wave plate, and of the irradiated blue P-polarized and S-polarized laser light, converts the P-polarized light to S-polarized light and emits all of the light unified to S-polarized light.
Polarization beam splitter 205 transmits yellow light, and regarding blue light, transmits the P-polarized component and reflects the S-polarized component, and the S-polarized blue laser light from polarization conversion device 202 is reflected and irradiated into phosphor wheel 101 by way of quarter-wave plate 201.
As shown in FIG. 3(a), in phosphor wheel 101, mirror 1011 that reflects incident light is formed on one portion, and phosphors 1012-1014 that are excited by incident light to emit yellow fluorescence are formed continuously in portions other than mirror 1011. When blue laser light is irradiated into mirror 1011, the light is reflected as is, and when irradiated into phosphors 1012-1014, yellow fluorescence is emitted. Because phosphor wheel 101 is rotating, blue laser light and yellow fluorescence are generated in a time series, and this light is irradiated by way of quarter-wave plate 201 into polarization beam splitter 205. At this time, when reflected by polarization beam splitter 205 and directed toward phosphor wheel 101, the blue laser light is S-polarized light, but subsequently, after having passed two times through quarter-wave plate 201, is irradiated into polarization beam splitter 205 in a P-polarized state. As a result, the blue laser light and yellow fluorescence that are in a time series both pass through polarization beam splitter 205 and are irradiated into color wheel 102.
As shown in FIG. 3(b), color wheel 102 is provided with regions 1021-1024 that make the color of transmitted light blue (B), green (G), red (R), and yellow (Y), and as a result, region 1021 corresponds to mirror 1011 of phosphor wheel 101, and regions 1022-1024 correspond to phosphors 1012-1014 of phosphor wheel 101. A diffusion plate is formed on region 1021 to which blue laser light is irradiated. Glass that transmits the transmitted light as is can be used in region 1024 to which yellow fluorescence is irradiated. For example, when the base plate of color wheel 102 is glass, the glass can be used without alteration. Of regions 1022 and 1023 to which yellow fluorescence is irradiated, a filter that transmits only G light is formed in region 1022, and a filter that transmits only R light is formed in region 1023. As a result, R, G, B, and Y light is emitted in a time series from color wheel 102.
The emitted light of color wheel 102 passes through rod integrator 208 and is uniformized, then turned back by mirrors 209 and 210 and irradiated into TIR prism 212, again irradiated into TIR prism 212 after undergoing modulation by DMD 104, and finally enlarged and projected by projection lens 213.
In the case of the optical system such as shown in FIGS. 1 and 2, phosphor wheel 101 and color wheel 102 must constantly be caused to rotate in synchronization at a timing in which regions 1021-1024 of color wheel 102 correspond to mirror 1011 and phosphors 1012-1014 of phosphor wheel 101.
In a spoke region where the same light beam is irradiated to a different regions of color wheel 102, a mixed color is generated, and as a result, this light cannot be used as R, G, and B light. FIG. 4(a) shows the sites at which spoke regions occur, and FIG. 4(b) shows a spoke region.
The light that is generated at spoke regions that are indicated by white circles in FIG. 4(a) can be used as white light and complementary colors (Cyan, Magenta, Yellow). The light (hereinbelow referred to as “RG”) that is generated in the spoke region between R and G as shown in FIG. 4(b) can be used as Y.
When making up white light without using light that is generated at a spoke region, i.e., when:White=Red+Green+Blue+Yellowthe gradation reproducibility is good, but the brightness is reduced because the light that is generated at a spoke region is not used.
When light that is generated in spoke regions is used to make up white light, i.e., when:White=Red+Green+Blue+Yellow+RG+GB+BY+YR(where GB is light generated between G and B, BY is light generated between B and Y, and YR is light generated between Y and R),all of the output light of color wheel 102 is used and the brightness of white light can be increased, but as a side effect, the possibility arises that the gradation reproducibility of an image worsens. This effect results because color is not uniform for light that is generated in spoke regions.
Compared to a projector in which the light source is configured using only a color wheel and without using phosphor wheel, the projector that is shown in FIG. 1 and FIG. 2 uses two wheels, and because divergence from synchronization caused by adjustment error of each wheel tends to occur, tends to suffer even greater deterioration in gradation reproducibility.
FIG. 5 shows the ideal light output in the projector shown in FIGS. 1 and 2, and in order to achieve ideal output such as shown in FIG. 5, control must be implemented such that the modulation operation of DMD 104 and the rotation operation of each wheel are synchronized.
As shown in FIG. 1, along with implementing control of the modulation operation of DMD 104 and receiving as input from phosphor wheel 101 and color wheel 102 Index signals S1 and S3 that indicate the rotational state of each wheel, control unit 103 detects the rotation operation of each wheel and implements control of the rotation operation of each wheel. The control of control unit 103 is next described with reference to FIG. 6.
On phosphor wheel 101 that is shown on the lower side of FIG. 6, mark 506 is provided at the position that is the emission start of Y (yellow) light at the time of the rotating state. Motor 505 that causes phosphor wheel 101 to rotate and detector 504 that detects mark 506 are provided on the side opposite the surface of incidence of the excitation light of phosphor wheel 101. On color wheel 102 that is shown on the upper side of FIG. 6, mark 503 is provided at the position that is the start of emission of Y (yellow) light during the state of rotating. Motor 502 that causes color wheel 102 to rotate and detector 501 that detects mark 503 are provided on the side opposite the surface of light incidence of color wheel 102.
Detector 504 is provided corresponding to the position of phosphor wheel 101 that is irradiated by excitation light and at which fluorescence or excitation light is emitted, and detector 501 is provided corresponding to an irradiation/emission position of color wheel 102 that is irradiated by light from phosphor wheel 101 and that emits B, G, R, and Y light in a time series.
Protuberances or holes can be used as marks 503 and 506, and photointerrupters or Hall elements can be used as detectors 501 and 504, but no particular limitations apply to these features.
The output of detectors 504 and 501 is supplied to control unit 103 as Index signals S1 and S3, and control unit 103 is thus able to detect that the irradiation/emission positions on color wheel 102 and phosphor wheel 101 are at the reference positions provided with marks 506 and 503.
Control unit 103 causes DMD 104 to display of B, G, R, and Y images in order, but in order to bring about the output of normal pictures, the reference positions of color wheel 102 and phosphor wheel 101 must be moved to the optimum positions in concert with the sequence of the DMD. Control unit 103 is able to implement rotation control that uses the reference positions of color wheel 102 and phosphor wheel 101, and in order to supply a normal picture, controls the rotational states of phosphor wheel 101 and color wheel 102 such that Index signal S3 is received from color wheel 102 when displaying an R image on DMD 104 and Index signal S1 is received from phosphor wheel 101 when displaying a B image on DMD 104.
The positions at which marks 506 and 503 are provided need not be the irradiation/emission positions on color wheel 102 and phosphor wheel 101, and further, the provided positions are also not limited to the emission start position of B light of phosphor wheel 101 and the emission start position of R light of color wheel 102. Even when the marks are provided to any positions on phosphor wheel 101 and color wheel 102, if the positional relation between the irradiation/emission position and the mirror or phosphors is well-defined for phosphor wheel 101, and if the positional relation between the irradiation/emission positions and each region are well-defined for color wheel 102, the illumination light obtained by phosphor wheel 101 and color wheel 102 can be matched with the modulation operation of DMD 104 shown in FIG. 6.
The above-described rotation control of the wheels that is matched with the image display presupposes that mark 506 is accurately formed between mirror 1011 and phosphor 1012 for phosphor wheel 101, that mark 503 is accurately formed between region 1023 and region 1022 for color wheel 102, and further, that the filter that is formed on color wheel 102 is accurately formed as designed. However, in actuality, due to error in manufacture, the phosphors, mirror, filters, and diffusion plates that are formed on each wheel may be fabricated at dimensions that differ from design, and in such cases, the ideal light quantity will not be supplied.
FIG. 7 shows the light quantity when mirror 1011 that supplies B and that is formed on phosphor wheel 101 is formed larger than region 1021 that is formed on color wheel 102. FIG. 7(a) shows the light quantity of one wheel rotation, and FIG. 7(b) shows an enlargement of the light quantity of the portion in which the required light quantity is not supplied.
As shown in FIGS. 7(a) and (b), B light is being supplied in the interval in which Y light is to be supplied from phosphor wheel 101. The B light that is supplied during this interval passes through the Y filter that is formed in region 1024 of color wheel 102, and the light quantity therefore decreases.
The size of the spoke region is determined by the beam diameter of a light beam that is incident to color wheel 102, but the range of error as shown in FIG. 7 is normally contained within a spoke region.
The decrease of the light quantity described above similarly occurs when the timing diverges for the interval in which B light is emitted in phosphor wheel 101 and the interval in which B light is transmitted in color wheel 102. FIG. 8 shows a state in which, despite the start of output of B from phosphor wheel 101, region 1021 of color wheel 102 is not synchronized and the B light is irradiated into the G filter of region 1022. In such cases as well, B passes through the G filter that is formed in region 1022 of color wheel 102, and the light quantity therefore decreases.
FIG. 9 is a figure showing a display example of a RAMP image (an image that gradually changes in luminance from 0 to 100% in the horizontal direction of the display screen). FIG. 9(a) shows the RAMP image realized by ideal light output such as shown in FIG. 5, and FIG. 9(b) shows the RAMP image realized by light output in which a decrease in light quantity occurs in a portion of the ideal light output as shown in FIGS. 7 and 8.
In the case of the light output in which there is a decrease in light quantity in a portion shown in FIG. 9(b), a fault occurs in which a belt-like image is displayed in portions of the vertical direction and a smooth change in gradation is not achieved. The cause for this is that light that is emitted in spoke regions is used as the light that makes up white light, whereby the decreases in light quantity generated in the spoke regions influence specific gradations of the RAMP image.
The examples shown in FIGS. 7 and 8 are examples in which mirror 1011 formed in phosphor wheel 101 is formed larger than region 1021 formed in color wheel 102.
Apart from the examples shown in FIGS. 7 and 8, decreases in light quantity that is generated in spoke regions may also occur when the output timing of Index signal S1 from phosphor wheel 101 diverges from the actual output timing of B light or when the output timing of Index signal S3 from color wheel 102 diverges from the actual output timing of the R light.
Factors that can be considered as causes of the divergence in timing described above include inaccuracy in the formation of mark 506 between mirror 1011 and phosphor 1012 in the case of phosphor wheel 101 and inaccuracy in the formation of mark 503 between region 1023 and region 1022 in the case of color wheel 102. Further, individual differences in the detection timing of detectors 504 and 501 can also be considered as a factor. Decrease of light quantity generated in a spoke region that results from divergence in timing is thus the main reason for decrease in the light quantity generated in a spoke region due to the large number of causes of occurrence.